1. Field of the Invention
The present invention is directed to self-cleaning linear ionizers and related processes for corona ionizers. The invention is particularly useful in (but not limited to) ionizing bars in which the linear ion emitter is a wire. Accordingly, the general objects of the invention are to provide novel systems, methods and apparatus of such character.
2. Description of the Related Art
Conventional linear ionizing bars are typically composed of: (1) a bar type ionization cell having at least one linear emitter and one or more non-ionizing reference electrode(s); (2) a clean air (or other gas) supply system having a group of jet type nozzles surrounding each ion emitter and connected to a supply manifold; and (3) a control system with an AC or pulsed DC high voltage power supply connected to the ionization cell. Such linear ionizing bars have found applications in a wide variety of manufacturing industries including flat panel displays, general electronics, semiconductors, etc. While some designs/applications may be optimized for ionization/charging, others may, instead, be optimized for charge neutralization. Charge neutralization applications may entail neutralization of large charged objects at relatively close distances and at rapid throughput rates. For example, the front and back of glass panels having a length and a width exceeding 3000 mm may need to be charge-neutralized wherein the distance between an ionizing bar(s) and the display panels usually ranges from 50-100 mm up to 1000 mm or more, and wherein the display panels are transported at high speeds using robotics systems.
Charge neutralizing bars with linear ionizers (ionizing cells comprising long thin wire(s) as emitter(s)/electrode(s)) have been suggested in (1) U.S. Pat. No. 7,339,778, entitled “Corona Discharge Neutralizing Apparatus”; (2) U.S. Pat. No. 8,048,200, entitled “Clean Corona Gas Ionization For Static Charge Neutralization”; and (3) U.S. Pat. No. 8,492,733 entitled “Multi-Sectional Linear Ionizing Bar And Ionization Cell”, all of which patents are hereby incorporated by reference in their entirety. Further, ionizing bars with wire emitters are currently produced by AB Liros Electronic of Malmö, Sweden and/or Liros Electronic of Hamburg, Germany, and Simco-Ion Technology Group of Alameda, Calif. USA.
With joint reference to FIGS. 1 and 2, a conventional multi-sectional linear ionizing bar 100 comprises four primary elements: a housing/enclosure 103, two ionization cells 101 and 102 with a stationary linear ion emitter 201 for establishing an ion plasma region along the length thereof, a manifold (hidden from view within housing 103) for receiving gas from a source and for delivering same past linear ion emitter 201, and means for applying 202 an ionizing signal/voltage (from a conventional/suitable power supply) to linear ion emitter 201 to thereby establish the ion plasma region. The ionization cells 101,102 also have common reference (non-ionizing) electrodes 104 and 105 positioned on both sides of the ion emitter 201. The electrodes 104,105 are conventionally positioned parallel to, on opposite sides of, and equally distant from ion emitter 201 This particular linear ionizing bar is shown and described in detail in U.S. Pat. No. 8,492,733 entitled “Multi-Sectional Linear Ionizing Bar And Ionization Cell” (incorporated by reference above).
As shown in FIGS. 1 and 2, housing 103 supports detachable ionization cell modules 101 and 102 from one side such that daisy-chaining of multiple cells together is easily accomplished. Enclosure 103 may house a high voltage power supply and control system within an interior side (bidden from view by the enclosure 103).
Each conventional ionization cell 101 and 102 may comprise a linear, for example, wire type corona discharge ion emitter/electrode 201, a pair of grills 205a and 205b, and an array (multiplicity/plurality) of gas orifices 206 positioned behind linear ion emitter 201 and through plate 203 for delivering gas steams past linear ion emitter 201 as shown.
It will be appreciated that the contact/tensioning springs 202 are preferably positioned at and affixed to each end of wire electrode 201 and to stationary cell 103. Springs 202 also receive high voltage ionizing signals and apply them to electrode 201. When such AC ionizing signals (typically, high voltage AC, but DC in certain applications) is applied to linear electrode 201, corona discharge occurs (between the electrodes 201 and 104,105) to thereby yield copious amounts of both polarity ions. As a result, emitter 201 is surrounded by dense, high-concentration bipolar ion cloud of positive and negative ions.
Despite the advantages of conventional linear ionizing bars of the type discussed above, they still suffer from at least one deficiency common among corona discharge ionizers: emitter corrosion/contamination/degradation which may significantly reduce ionizing bar performance by causing an undesirable ion balance offset, longer discharge times, and the spread of contamination to the ambient environment and the target workpiece(s). Therefore, manual and regular emitter cleaning is a mandatory maintenance requirement for linear ionizing bars of the type discussed above. In this design, wire emitter is elevated above base plate 203 by the spring arrangement to facilitate manual removal of corrosion, debris, dust, etc. that accumulates on wire electrode 201.
Manual cleaning is undesirable for a number of reasons. For example, the manual cleaning process requires turning off the flow of air/gas and the high voltage ionizing signals and inserting some type of wire cleaning implement between two grills/rails 205a and 205b. This cleaning implement may be a brush, a wet/dry wipe, or a foam block that physically contacts emitter wire 201 as it is rubbed back and forth along emitter 201. The cleaning implement may be connected to a stick to reach emitter wire 201 from a relatively long distance because it is often difficult to reach the ion emitter wire for manual cleaning especially for ionizing bars installed in large semiconductor tools. For this reason, manual cleaning may damage the wires, spring contacts, and shorten lifetime of the detachable ionization cells. Last but not least, the frequency with which cleaning cycles must occur depends on the ambient air conditions/cleanness (such as airborne particulate concentration or airborne molecular contamination (AMC)) of rooms/production floors in which the ionizing bars are used. Such cleaning cycles may be time-consuming and may be required daily or weekly in certain critical field-applications.